<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <meta http-equiv="X-UA-Compatible" content="ie=edge" />
    <title>CSS3属性calc函数</title>
    <style>
      .father {
        width: 300px;
        height: 200px;
        background-color: pink;
      }
      .son {
        /* width: 150px; */
        /* width: calc(150px + 30px); */
        width: calc(100% - 30px);
        height: 30px;
        background-color: skyblue;
      }
    </style>
  </head>
  <body>
    <!-- 需求：子盒子宽度永远比父盒子小30像素 -->
    <div class="father">
      <div class="son"></div>
    </div>
  </body>
</html>
